Lecithins have been known for many years as valuable agents for the fat-liquoring of leather. For use in fat-liquoring baths, lecithins are emulsified with known anionic, cationic, or nonionic emulsifiers. Frequently, anionic, cationic, and nonionic leather oils are used in combination with lecithins.
In a series of German patents, agents for the fat-liquoring of leather are described. The agents cited consist of a mixture of lecithins and fatty oils or fish oil. In certain patents of addition, the variation of agents resides in the addition to the mixture of a multiple amount of water or slight quantities of soaps or sulfonated oil. The aforementioned agents are described in detail in the principal patent DE-PS No. 514 399 and in the corresponding patents of addition DE-PS No. 516 187, DE-PS No. 516 188, DE-PS No. 516 189 and DE-PS No. 522 041.
In DE-OS No. 31 01 914, partially saponified lecithins having a saponification number of 120-140 are disclosed in admixture with polyhydroxyl compounds (sugar and the like) as auxiliary agents for textiles, paper, and leather, used particularly in formulations containing nonionic or anion active emulsifiers, and also with organic solvents.
It is further proposed in DE-AS No. 28 43 755 to use a hydroxylated phosphatide for the fat-liquoring of tanned leather.
The above cited patents indicate that lecithin, in view of its chemical structure (it consists of a fatty substance with polar groups), is a readily applicable leather fat-liquoring agent. Experience shows, however, that in emulsions it forms large micelles, so that its penetration into the leather is incomplete. The use of lecithin is therefore restricted in actual practice, as frequently the leather is inadequately oiled and the finished leathers are stiff and excessively hard.
The essential condition of the use of lecithin is to employ a formulation whereby the leather is penetrated completely and uniformly by the fat-liquoring agent and the liquor bath is depleted efficiently and as completely as possible.